Method for detecting closure of a solenoid coil from the rise time of each of the current peaks of the solenoid coil

A method for detecting closure of a first solenoid coil in a solenoid arrangement comprising first and second solenoid coils and a solenoid armature that moves between the first and second solenoid coils, the solenoid arrangement further comprising a switch coupled in series with the second solenoid coil between a supply voltage terminal and a reference voltage terminal, the method comprising the steps of:

• providing a holding current signal to the first solenoid coil to maintain the solenoid armature in an initial closed position with the first solenoid coil;
• providing a PWM control signal to the switch to control the opening and closing of the switch such that a pulling current signal, comprising a plurality of current peaks, is established in the second solenoid coil, each of the current peaks having a measurable rise time which is dependent on the width of the corresponding pulse of the PWM control signal;
• storing a value representative of the width of a PWM control signal pulse for one of the plurality of current peaks;
• removing the holding current signal from the first solenoid coil;
• sensing the width of the PWM control signal pulse for each of the current peaks in the second solenoid coil and determining when the sensed width changes from the stored width by a predetermined amount which indicates that the solenoid armature has started to move towards the second solenoid coil;
• continuing to sense the width of the PWM control signal pulse for each of the current peaks in the second solenoid coil;
• and
• providing an indication that the solenoid armature is in a closed position with the second solenoid coil when the sensed width of a PWM control signal pulse returns to substantially the same value as the stored width.